In existing drive trains for marine engines, such as those using transmissions manufactured by Borg-Warner Automotive Inc. or Hurth Axle S.p.A., it is necessary to provide some cushioning of shock between the transmission and the engine drive plate. For example, Carlson U.S. Pat. No. 2,993,544 shows the use of rubber cushions to cushion shock between the drive shaft and a boat propeller of an outboard motor. Perrot U.S. Pat. No. 3,045,763 shows a similar arrangement in which the rubber cushions form blocks sitting on top of lugs or ribs. Shepherd U.S. Pat. No. 3,645,114 discloses a flexible rotary drive train in which there is a splined coupling having rubber cushions interposed between the splines. Other cushioned drivelines are shown in U.S. Pat. Nos. 1,552,892; 1,974,356; 3,411,323; 4,194,373; and 4,747,796.
In the past this cushioning of shock between the transmission and the engine drive plate has been most commonly accomplished by using a clutch-like drive ring mounted on the drive plate and which uses an array of springs to dampen shock. The drive shaft connected to the transmission has a splined end which fits into the complementary splines in the centre of the drive ring. As these splines wear, however, the fit becomes loose and the tendency to wear increases, eventually resulting in stripping of the splines and failure of the drive train.
A further solution to the drive problem has been the use of a drive ring which incorporates a "spider drive" having a number of lugs with rubber blocks which fit in corresponding slots in the drive ring. The rubber blocks absorb shock as between the engine and the transmission. These types of drive are manufactured by Twin Disc Inc. of Racine, Wis. Again, however, either a free-floating spline shaft, or a tapered shaft drawn into the centre of the spider drive by a bolt are used and wear problems can still persist. Also, the spider drive incorporates rectangular lugs within rubber blocks having a trapezoidal outer shape to conform to the drive ring. This causes uneven wear on the rubber blocks.